Two-source interference can be demonstrated using water ripples, sound,light and microwaves For two-source interference fringes to be observed the waves from the two sources must be coherent(constant phase difference)and must meet (superpose)with a path difference of nλ(n =0.1, 2... or phase difference of 0,360°,720°… or 02n radians, 4 radians.. for maxima and (n+1/2)λ (n =0, 1,2...) or phase difference of 180° 540°,900°… or 𝝅 radians, 3𝝅 radians,5𝝅 radians… for minima.